DESCRIPTION (taken from abstract): Visual perception and resulting actions derive from interactions amongst neurons that are organized as parallel pathways that parse out specific computational tasks. In mammals, experimental access to these neural substrates is limited by factors such as size, subject availability, and economics. An alternative system that elegantly demonstrates how identified neurons interact to process fundamental features of the visual world, such as motion, is provided by the dipteran visual system. This model, like its mammalian counterpart, possesses a system of achromatic magnocellular neurons that carry information about motion to a center controlling optokinetic behavior. There is also a second, parallel system of parvocellular neurons that supply a cortex-like area in the brain encoding information about pattern, orientation, and color. In-depth analysis and predictive modeling of functionally identified neurons that comprise these two subsystems are now providing fundamental insights into the synaptic arrangements and neural mechanisms that underlie the control of head movements and the analysis of form and color. The proposed research will investigate: Neural mechanisms and circuit properties amongst achromatic neurons that (a) compute the first stages of motion detection, (b) integrate motion information with object detection to provide target-directed head movements, saccades, and distance perception, and (c) control saccadic head movements by integrating them with proprioceptive reafference that monitors head movements. Neural mechanisms and circuit properties amongst parvocellular neurons that separately and collectively discriminate orientations, textures, and color. The research emphasizes intracellular recordings, confocal studies of dye-filled neurons, synaptology, and identification and localization of neurotransmitters. Models to (a) test the functional properties of synaptic circuits amongst recorded and identified neurons, (b) direct novel experiments, and (c) serve as a basis for reverse engineering of this model visual system. A complete functional and computational understanding of the dipteran system will provide crucial insights into basic principles of visual processing and will provide essential information for constructing miniaturized prosthetic visual systems and automata.